One common thread is a skepticism about the value science, and particularly the value of the scientific establishment.

Some believe that science simply doesn't apply. "Healing fields", they say, cannot be detected by science; indeed scientific analysis may destroy them. Herbal remedies are safe because Nature loves us. Yahweh promised us the Earth, so it's impossible for us to render it (transiently) inhospitable.

This version of anti-science is uninteresting. These arguments can't be refuted for the same reasons that we can't disprove the existence of unicorns and leprechauns. There's no measure for resolving disagreements; these are theological disputes.

Another form of argument grants that the scientific method is effective, but claims that the scientific establishment is corrupt and untrustworthy. This is more interesting because it's at least partly true. Over the past twenty years we've learned about the effects of publication bias, particularly when corporations with strong financial interests (ex: Pharma) control the publication of research results. We've seen some spectacular scientific frauds, and we've seen a trend to "me too" research that gets safe grants but produces small results. During the Bush years, we saw loyalists suppress scientific results their bosses disliked.

Alas, there's no evidence the amateurs are reliable; most seem driven by the same passions that power crank cosmologists. Even if they were angels, furthermore, by their nature these amateurs bypass scientific evaluation and challenge. They cannot be judged because they're not in the game.

Sure, the scientific program is imperfect, but, when it comes to understanding the world, there are no alternatives. The process of iterating on internally consistent models that make testable predictions, and revising those models when predictions fail, has transformed human history. It is the only guide we have to developing better medicines, understanding the universe, or predicting the consequences of CO2 accumulation.

The denialists do have a point, even if they don't fully recognize it. We can and should improve the machinery of science. Requirements to publish data obtained through public investments, registries of studies to ensure negative and unfavorable results are published, and (more challenging) reforms to grant programs and academic tenure are some of the improvements seen over the past decade.

Science tells us Homeopathy's effects are mediated by belief, not molecules. Science tells us that CO2 accumulation will change the earth's climate; and that these changes will be extremely disruptive for a crowded planet with fixed borders.

Maybe in ten years science will tell us that solar cycles are more important for our 21st century climate than CO2 accumulation. Maybe science will tell us that spinal manipulations do change the immune system. Maybe, but probably not.